The present invention relates to a surface mount self-induction component which is used in, for example, a transmitting and receiving circuit, a noise filter, a current detection circuit that are useful in a portable telephone, a video camera, a computer, and the like, and more particularly to a common mode filter.
As a surface mount self-induction device of the prior, known are a device such as a common mode filter 300 of FIG. 12 in which a drum core 100 and a tubular core 200 are combined with each other to form a closed magnetic path, and a device having a structure in which external electrodes are formed on a resin sheath and a winding wound around a core is connected to the electrodes.
Recently, miniaturization of an electronic apparatus is rapidly advancing. As a result, also a surface mount self-induction component such as an inductor which is an internal component of an electronic apparatus is requested to be further miniaturized.
However, the configuration of a component such as the common mode filter 300 of FIG. 12 hardly fulfills such a request. Namely, the tubular core 200 and the resin sheath are restricted in size and hence it is very difficult to miniaturize the component in a large degree.
In order to comply with the above, miniaturized surface mount self-induction components are proposed in Japanese Patent Publications (Kokai) Nos. HEI8-213248 (shown in FIG. 13) and HEI8-186028.
The surface mount self-induction component shown in FIG. 13 is a chip inductor. Electrodes 20A and 20B each configured by a film-like conductor are formed on the lower faces of end flanges 30A and 30B of a magnetic core 10 which is a molded product of a metal oxide, respectively. A winding 40 is connected to the electrodes. A heat resisting film 50 is joined to the upper face of the winding 40 by an adhesive agent 60 so as to bridge the upper faces of the flanges 30A and 30B. By contrast, the surface mount self-induction component of Japanese Patent Publication (Kokai) No. HEI8-186028 is a wound chip inductor having a gap. The publication shows that the invention is configured by forming a flange having a cross section shape on each of the opposed ends of a winding shaft of a core of the closed magnetic path type, directly forming an electrode on a lower side face of each of the opposed cross flanges, connecting terminals of a winding wound around the winding shaft to the electrodes, and attaching an I-core to upper portions of the flanges via a gap forming medium.
In the induction components disclosed in the publications, the size restrictions due to a tubular core and a resin sheath are not imposed, and hence the components can be miniaturized.
Recently, particularly in a portable electronic apparatus or the like (for example, a portable CD player, a portable MD player, or a portable information terminal), the thickness of the apparatus is extremely reduced as miniaturization of the apparatus is advancing. Therefore, a surface mount self-induction component serving as an internal component must be configured so as to be thinner. With respect of this point, the prior art components of FIG. 13 and Japanese Patent Publication (Kokai) No. HEI8-186028 have the following problems.
In the induction component of FIG. 13, terminals of the winding are connected to the lower-face electrodes formed on the lower faces of the flanges. As the wire of the winding has a larger diameter, therefore, the height of the component is larger.
By contrast, in the induction component of Japanese Patent Publication (Kokai) No. HEI8-186028, the electrodes are formed directly on the lower side faces of the opposed cross flanges, and the winding is connected to the electrodes. As the winding has a larger diameter, therefore, the heights of the lower side faces of the flanges are larger, with the result that the total height of the component becomes larger. It may be contemplated to employ a configuration in which the winding core is made smaller in diameter so that the winding can be made thicker without changing the total height of the component. When the winding core is made smaller in diameter, however, the inductance becomes smaller so that the properties are impaired. Therefore, this configuration is not preferable. Moreover, the connecting positions of the winding exist on the lower side faces of the cross flanges. Consequently, the connection of the winding is hardly performed by means of machinery, and hence the productivity is poor.
Because of these reasons, thinning of a surface mount self-induction component of the prior art inevitably causes the diameter of a winding to be reduced. As a result, the current capacity is reduced.
Even in the above-mentioned field of an electronic apparatus where thinning is particularly advancing, however, a part of surface mount self-induction components are often required to have a large current capacity. In order to trap noises before entering an electronic apparatus and diffusing therein, for example, a surface mount self-induction component which is used for eliminating noises, such as a common mode filter is preferably used also in an input/output portion of the electronic apparatus. Usually, a very large current (about 2,000 mA) flows in an input/output portion of an electronic apparatus.
Particularly in the field of an electronic apparatus, therefore, it is eagerly requested to develop a surface mount self-induction component which can cope with thinning of an electronic apparatus and which has a sufficient current capacity. However, the prior art cannot sufficiently satisfy such a requirement. In order to improve not only the properties but also the productivity, moreover, it is requested to facilitate the production of such a component by means of machinery. However, the prior art hardly copes with automation.